Method of manufacturing a tubular medical implant

ABSTRACT

A method of manufacturing a tubular medical implant is provided. The method includes forming a hollow first tube with a first diameter and a first plurality of pores formed thereon and a hollow second tube with a second unstretched diameter and a second plurality of pores formed thereon. The second unstretched diameter is greater than the first diameter. At least a portion of the first tube slides within the second tube to create an overlapped area of the first tube and the second tube. The first tube and second tube are then bonded together in the overlapped area.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a non-provisional application based upon U.S. provisional patentapplication Ser. No. 61/788,738 entitled “POROUS TUBES”, filed Mar. 15,2013, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing medicalimplants, and, more particularly, to a method of manufacturing tubularmedical implants.

2. Description of the Related Art

Medical implants are manufactured incorporating various techniques toproduce different shapes using biologically compatible materials. Onemedical implant shape that is commonly used is that of a tubularstructure. Tubular medical implants have a wide range of medicallyuseful applications in orthopaedics, cardiology and other areas. Oneuseful feature incorporated into tubular medical implants is a porepattern on the surface and throughout the implant. By incorporatingporosity into the tubular implant, the implant can be given usefulproperties such as controlled therapeutic release and/or an interfacefor cell or tissue growth.

As cell growth mechanics and pharmacokinetics have become betterunderstood, the pore structure of medical implants have becomeincreasingly complex and structured. Such designs requirements ofincreased complexity have not been met by current production methods,especially in tubular implants that have a relatively high thicknessand/or highly variable pore pattern throughout the implant. Ofparticular difficulty is varying the implant's pore pattern throughoutthe thickness of the tubular implant.

One known method of producing tubular medical implants with variedporous structures is to take a base tube, such as a stent, and stretchan elastic, porous graft material over the stent. When the graftmaterial is properly positioned over the tube, the stretching force isremoved which allows the graft material to return to a less stretchedstate and form a snug fit on the stent. The graft material can then besewn on to the graft to create a finished stent graft. A problem withthis method is that it limits the materials that can be incorporatedinto the medical implant, is labor intensive and has the risk ofpermanently changing the pore sizes on the graft material duringstretching.

What is needed in the art is a method that can manufacture tubularmedical implants that have complex porous structures from a largevariety of materials.

SUMMARY OF THE INVENTION

The present invention provides a method of creating a tubular medicalimplant by sliding at least a part of a first porous tube within asecond porous tube to create overlapped areas between the first andsecond porous tubes and then bonding the overlapped areas together.

The invention in one form is directed to a method of manufacturing atubular medical implant including the step of forming a hollow firsttube with a first diameter and a first plurality of pores thereon. Ahollow second tube is formed with a second unstretched diameter and asecond plurality of pores formed thereon. The second unstretcheddiameter is greater than the first diameter. At least a portion of thefirst tube is slid within the second tube to create overlapped areasbetween the first tube and the second tube, which are bonded together.

The invention in another form is directed to a tubular medical implantthat includes a first hollow tube, a second hollow tube, and a bondinginterface. The first hollow tube includes a first surface with a firstplurality of pores formed thereon and the first hollow tube defines afirst diameter. The second hollow tube surrounds the first hollow tubeand includes a second surface having a second plurality of pores formedthereon. The second hollow tube defines a second unstretched diameterthat is greater than the first diameter of the first hollow tube. Abonding interface is formed between the first hollow tube and secondhollow tube to hold the hollow tubes together.

An advantage of the present invention is that it provides a method toproduce tubular medical devices that have complex porous patterns.

Another advantage is that the method of the present invention allows forprecise control of the pore size and distribution in the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of a porous tube of the present invention;

FIG. 2 is a perspective step-by-step view of a method of producing atubular medical implant according to the present invention;

FIG. 3 is a perspective view of the tubular medical implant produced bythe method shown in FIG. 2;

FIG. 4 is a close-up perspective view of a porous tube of the presentinvention;

FIG. 5 is a sectional side view of the porous tube shown in FIG. 4 alongline A-A;

FIG. 6 is a close-up perspective view of another tubular medical implantproduced according to the present invention;

FIG. 7 is a sectional side view of the tubular medical implant shown inFIG. 6 along line A-A;

FIG. 8 is a close-up perspective view of another porous tube of thepresent invention;

FIG. 9 is a sectional side view of the porous tube shown in FIG. 8 alongline A-A;

FIG. 10 is a close-up perspective view of yet another tubular medicalimplant produced according to the present invention;

FIG. 11 is a sectional side view of the tubular medical implant shown inFIG. 10 along line A-A;

FIG. 12 is a close-up perspective view of yet another porous tube of thepresent invention;

FIG. 13 is a sectional side view of the porous tube shown in FIG. 12along line A-A;

FIG. 14 is a close-up perspective view of yet another porous tube of thepresent invention;

FIG. 15 is a sectional side view of the porous tube shown in FIG. 14;

FIG. 16 a perspective step-by-step view of a method of producing anothertubular medical implant according to the present invention; and

FIG. 17 is a perspective view of the tubular medical implant produced bythe method shown in FIG. 16.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown a hollow tube 20 which generally includes a tube wall 22 and pores24 formed in the tube wall 22. As can be seen, the hollow tube 20 hasmany pores 24 formed through its tube wall 22, but the number of pores24 can be varied depending on the tube's 20 intended application. Thetube wall 22 has a thickness that can be the same throughout the tube 20or varied. The tube wall 22 can have any thickness suitable for use at adesired implantation site, including a range from about 0.0001″ togreater than 0.04″. The tube 20 can be made from any suitablebiocompatible material, e.g., titanium, titanium alloys, tantalum,tantalum alloys, cobalt chrome alloys, stainless steel,polyaryletherketone polymers (PAEK), polyetheretherketone (PEEK),polyetherketone (PEK), polyetherketoneketone (PEKK), Ultrapek,polyethylene, polyurethane, alumina and zirconia. Once the tube 20 isformed, the pores 24 can be created in the tube wall 22. The pores 24can be created by a variety of processes, e.g., chemical etching,photochemical etching, laser cutting, electron-beam machining,conventional machining, stamping, extrusion, rolling and knurling.

Referring now to FIG. 2, multiple tubes 20, 26, 28, 30 are shown. Eachtube 20, 26, 28, 30 has a respective unstretched diameter d1, d2, d3, d4and a tube wall 22, 32, 34, 36 with pores 24, 38, 40, 42 forming porepatterns 44, 46, 48, 50. The tubes' diameters d1, d2, d3, and d4 vary,with d1<d2<d3<d4. Preferably d1 is not substantially less (>5%) than d2,d2 is not substantially less than d3, and d3 is not substantially lessthan d4. Each tube wall 22, 32, 34, 36 has a respective thickness thatmay or may not be equal to the thickness of the other tube walls. Eachtube 20, 26, 28, 30 can be made from the same material or differentmaterials, depending on the implant's intended application.

To produce a finished porous tubular implant 52 (shown in FIG. 3), thetubes 20, 26, 28 with smaller diameters d1, d2, d3 are placed into thetubes 26, 28, 30 with larger diameters d2, d3, d4 sequentially, andbonded together. For example, tube 20 would first be placed within tube26 to produce a tube (not shown) that has a tube wall thicknesssubstantially equivalent to the thicknesses of tubes 20 and 26 addedtogether. The produced tube also has a 3-dimensional pore architecturethat is a combination of pore patterns 44 and 46. Once tube 20 is placedwithin tube 26, overlapped areas 54 (shown in FIG. 3) of the tubes 20,26 are created that can be bonded together to hold tubes 20 and 26together, if desired, before the intermediate tube is placed within tube28. Preferably, the diameters d1 and d2 of the tubes 20 and 26 will berelatively similar to each other to allow for a bond interface 56 (shownin FIG. 3) with a negligible thickness or effect on an implant porepattern 58 of the finished porous tubular implant 52. Once tube 20 iswithin tube 26, either bonded or not, the tubes 20, 26 are then placedwithin tube 28, and optionally bonded to tube 28 at overlapped areas.Once tubes 20 and 26 are within tube 28, and optionally bonded, thetubes 20, 26 and 28 are placed within tube 30 and bonded at overlappedareas to form finished tubular implant 52. While finished tubularimplant 52 is shown as having the tubes 20, 26, 28 and 30 completelyoverlapping, it could be desirable to create a tubular implant that hasonly a partial overlap between some or all of the various componenttubes. As previously mentioned, a bond interface 56 is formed betweentubes that are bonded together. The bond interface 56 can be formed bythe material of tube walls pressing together or be a separable bondingcomponent, such as an adhesive. The method used to bond tubes togethercan vary based on the tube material(s), but can include, e.g., diffusionbonding, sintering, laser welding, heat staking, thermal processing,ultrasonic welding, mechanical welding and adhesive bonding.

FIGS. 4 and 5 show one embodiment of a section of a tube 60 according tothe present invention. FIG. 4 shows a porous microstructure 62 of thesection of a porous thin-walled tube 60 of wall thickness T. For ease ofexplanation, tube wall 64 is displayed as flat rather than curved. Allpores 66 in this tube wall 64 are through-holes. Struts 68 (which can bereferred to as scaffold struts) are defined as the bars of materialbetween the pores 66. Strut width W is defined as the smallest dimensionof an individual strut 68 on the tube 60 surface. FIG. 5 shows asectional view of the porous tube 60 in FIG. 4 along line A-A.

FIG. 6 shows a section of a resulting porous microstructure 70 of poroustubular implant 52 and FIG. 7 shows a section taken along line A-A inFIG. 6. FIG. 7 thus shows one tube wall 72 including four thin-walledtubes 20, 26, 28, 30. The other side of the tube 72 across the diameterof the tube 72 is not shown in FIGS. 6 and 7; in other words, thelongitudinal axis of the thin-walled tube can be, for example, to theright of the sectional view in FIG. 7, and the longitudinal axis of theassembled tube 72 can be, for example, to the right of the sectionalview in FIG. 7.

FIGS. 8 and 9 shows another embodiment of a tube 80 according to thepresent invention. FIG. 8 shows a porous microstructure 82. FIG. 9 showsa portion of a porous thin-walled tube 80 of wall thickness T. For easeof explanation, the tube wall 84 is displayed as flat rather thancurved. Pores 86 are then created in the tube 80 from both sides 88, 90of an individual thin-walled tube 80. Different patterns are used tocreate the pores 86 on each side 88, 90 of the tube 80. A first porepattern 92 from the outside of the tube 80 transitions to a second porepattern 94 from the inside of the tube 80 at some location 96 within thetube wall 84. This location 96 is defined as A*T, where coefficient A issome fraction of the wall thickness. Coefficient A can range from justgreater than 0 to just less than 1. Typically, coefficient A will mostlikely be on the order of 0.35-0.65.

To generate a three-dimensional porous tube 100 as shown in FIG. 10,individual thin-walled tubes such as in FIG. 8 are bonded together. Inthis embodiment of the invention, pore patterns 101, 102, 104, 106 areformed on adjacent sides of adjacent tubes 108, 110, 112 (see FIG. 11).For the three thin-walled tubes 108, 110, 112 bonded together, shown inFIG. 11, tube 108 has pore pattern 101 on a first side 114, and porepattern 102 on a second side 116. Tube 110 has pore pattern 102 on afirst side 118 and pore pattern 104 on a second side 120. Tube 112 haspore pattern 104 on a first side 122 pore pattern 106 on a second side124. Thus, adjacent thin-walled tubes 108, 110, 112 mate up againstidentical pore geometries. While the pore patterns 101, 102, 104, 106 ofthe thin-walled tubes 108, 110, 112 are shown in FIG. 11 as beingaligned to identical pore patterns on adjacent thin-walled tubes 108,110, 112, the present invention also contemplates mating a tube toanother tube with an identical pore pattern on a first side of the tubeand a different tube with a non-identical pore pattern on a second sideof the tube. The pore patterns 101, 102, 104, 106 can all overlap tocreate an implant pore (unnumbered) that extends completely through theformed tube wall of porous tube 100.

FIGS. 12 and 13 show another embodiment of a tube 130 according to thepresent invention. Within a given thin-walled tube 130 of wall thicknessT, as can be seen in FIG. 13, the geometry adjacent to a surface 132 canbe denoted as a first pore pattern 134. At a thickness of A*T, wherecoefficient A is some fraction of the tube wall thickness T, first porepattern 134 transitions to a second geometry (pore pattern) 136.Likewise, at a thickness of B*T, where coefficient B is some fraction ofthe tube wall thickness T, second pore pattern 136 transitions to athird geometry (pore pattern) 138. The values of coefficients A and Bare such that 0<A<B<1. The third pore pattern 138 can be different fromor identical to the first pore pattern 134.

The method of the present invention contemplates any number of differentgeometries being included in a tube wall. FIGS. 14 and 15 show a tubewall 140 with five different geometries 142, 144, 146, 148, 150 througha wall thickness T. Geometries 142, 144, 146 and 148 can have respectivefraction coefficients A, B, C, D of thickness T that represent thefractional thickness of the corresponding geometry, which can be definedby 0<A<B<C<D<1. Thus, the thickness of geometry 142 is A*T, thethickness of geometry 144 is B*T, the thickness of geometry 146 is C*T,and the thickness of geometry 148 is D*T.

As described throughout, the number of tubes that can be bonded togetheraccording to the present invention to form a porous tubular implant canbe varied from a small number (2) of tubes to a large number (>10) oftubes.

The present invention in one form provides a bone or tissue scaffoldincluding a plurality of layers bonded to one another, each layer havinga different pore pattern formed on each side of the layer, adjacentsides of adjacent layers having substantially identical pore patternswhich thus align with one another over the course of at least two (forexample, two, three, or more) adjacent layers, each layer being formedas a tube, each tube being concentric relative to the other tubes.

Clinically acceptable bone ingrowth or on-growth surfaces such asBioSync ™ marketed by Sites Medical, beads, plasma spray, or othersimilar bone or tissue ingrowth or on-growth surfaces can be used.

The manufacturing method described herein may be used for other purposesas well. One alternative use of this method includes creating astructure that has a layer(s)/tube(s) that is not porous all the waythrough, or that when aligned (for example, a respective layer) with anadjacent layer a barrier is created to prevent bone or other material,such as a lower melting temperature material, from passing through. Inthis way, to one side of the barrier, tissue ingrowth can occur; to theother side of the barrier, the lower melting temperature material (whichcan form a structure beyond the pores) can be retained in the pores.

Another alternative use of this method includes creating a structureincluding a layer(s)/tube(s) in the “middle” which has recesses and/orporous sections and including outer layer(s)/tube(s) which are generallysolid. The purposes of this include the following: (a) to create amaterial or product that is lighter by removing material from the wallthickness while leaving the outer or working surfaces unaffected; (b) tocreate a material or product that has more flexibility and strength in alighter weight configuration than otherwise possible because of theother size constraints; (c) to provide a method to create regions insideof a product for storage of different materials for a variety ofpurposes, both medically and non-medically related. While this method isdescribed in the general application of a tube, this feature can beapplied to flat, curved, or other similar geometries.

FIGS. 16 and 17 illustrate a tubular medical implant 160 incorporatingporous tubes 162, 164, 166 and a non-porous tube 168. Porous tube 162 isplaced within porous tube 164, and optionally bonded together, beforebeing placed within non-porous tube 168. Non-porous tube 168 can act asa barrier to prevent ingrowth of tissues into porous tubes 162 and 164,but can also act as a support tube when placed within porous tube 166 ifother tubes (not shown) are being press fitted to porous tube 166. Insuch a case, non-porous tube 168 can provide strength to resist collapseof porous tube 166 when a pressing pressure and a pressing temperatureare applied to the porous tube 166 to press fit another tube on toporous tube 166. Non-porous tube 168 could also be a solid tube actingas a core for porous tubes stacked on top.

Further, in another embodiment of the present invention, the scaffold ofthe present invention can be attached (for example, by way of diffusionbonding) to a substrate (such as an implant). The substrate can be animplant and can be made of a variety of materials, including, but notlimited to, titanium and/or CoCr.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

What is claimed is:
 1. A method of manufacturing a tubular medicalimplant, comprising the steps of: forming a hollow first tube having afirst diameter and a first plurality of pores formed thereon; forming ahollow second tube having a second unstretched diameter and a secondplurality of pores formed thereon, said second unstretched diameterbeing greater than said first diameter; sliding at least a portion ofsaid first tube within said second tube to create an overlapped area ofsaid first tube and said second tube; and bonding said first tube tosaid second tube in said overlapped area.
 2. The method according toclaim 1, wherein said first plurality of pores forms a first porepattern and said second plurality of pores forms a second pore pattern.3. The method according to claim 2, wherein said first pore pattern andsaid second pore pattern are different patterns.
 4. The method accordingto claim 2, wherein said first pore pattern and said second pore patternare the same pattern.
 5. The method according to claim 2, wherein saidbonding step is accomplished using at least one of diffusion bonding,sintering, laser welding, heat staking, thermal processing, ultrasonicwelding and adhesive bonding.
 6. The method according to claim 2,wherein said bonding step is accomplished by pressing said first tubeand said second tube together at a bonding temperature and a bondingpressure.
 7. The method according to claim 6, further comprising thestep of providing a support rod within said first tube prior to saidbonding step.
 8. The method according to claim 2, wherein said secondtube is in a substantially non-deformed state when sliding over saidfirst tube.
 9. The method according to claim 2, further comprising thestep of aligning said first pore pattern relative to said second porepattern prior to said bonding step to form an implant pore pattern. 10.The method according to claim 9, wherein said first tube is composed ofat least one of a polymer, a metal and a ceramic and said second tube iscomposed of at least one of a polymer, a metal and a ceramic.
 11. Themethod according to claim 10, wherein said implant pore pattern includesat least one pore formed through said implantable tubular structure. 12.The method according to claim 10, wherein said first tube and saidsecond tube are aligned such that said first pore pattern and saidsecond pore pattern have no overlap.
 13. The method according to claim2, wherein said first pore pattern and said second pore pattern arecreated by using at least one of chemical etching, photochemicaletching, laser cutting, electron-beam machining, conventional machining,stamping, extrusion, rolling and knurling.
 14. A tubular medicalimplant, comprising: a first hollow tube including a first tube wallwith a first plurality of pores formed thereon, said first hollow tubedefining a first diameter; a second hollow tube surrounding said firsthollow tube to form an overlapped area and including a second tube wallwith a second plurality of pores formed thereon, said second hollow tubedefining a second unstretched diameter that is greater than said firstdiameter; and a bonding interface between said first hollow tube andsaid second hollow tube at said overlapped area.
 15. The tubular medicalimplant of claim 14, wherein said first plurality of pores forms aninner pore pattern and said second plurality of pores forms an outerpore pattern.
 16. The tubular medical implant of claim 15, wherein saidinner pore pattern and said outer pore pattern together form a pluralityof implant pores forming a tubular implant pore pattern.
 17. The tubularmedical implant of claim 16, wherein a plurality of said implant poresextend entirely through said porous tubular implant.
 18. The tubularmedical implant of claim 17, wherein at least one of said plurality ofimplant pores is formed by a partial overlap of one of said firstplurality of pores and one of said second plurality of pores.
 19. Thetubular medical implant of claim 18, wherein said bonding interface isat least one of an adhesive, a deformed material and a melted material.